Other than fillable forms, which is sometimes very important, I don't see how PDF is much of an improvement over PostScript (which came first).
PDF would have a similar problem, but Adobe leveraged their previous work on other products so they basically already had the rendering engine for Windows and it gained traction there.
Keep in mind that both Postscript and PDF were principally designed by Adobe. Adobe designed both because they were intended for different purposes, and this stands today.
Except it's not Xorg but Sun's own server, and it's not Linux but Solaris.
Far as I can tell, most of the time (all of the time?) PDFs just seem to throw out this information, and manually select and place glyphs.
A work colleague worked on a document signing solution for a client once. Legally, at the time (and I hope this has improved), when a person added their digital signature to a document, that meant that they signed that exact version (read: hash of all the bytes) of the document.
That meant that PDF was sort-of problematic for the use case that the customer required: Giving the customer an A4 version to keep for their documentation was important - but having an A4 version on screen made for terrible scaling UX on mobile and tablet devices.
The fact that PDF is more than just text+formatting in that manner was a real hindrance at that point in time (2017).
(I'd be happy to know if I got any of this wrong after only hearing about it second-hand. This was in Switzerland, if this affects which laws were relevant at the time.).
It turns out to be a feature where adding a "signature" locks the document. They suggest if you need to modify it you request a new document.
I'm probably reading the spec wrong, but it might have been added in PDF 1.5 (Aug 2003?)
I think the concept is great and was just passing along that it existed in PDFs to the parent. Personally, having signed probably 100s of PDFs over the years I had never encountered it. I've only seen the web-based DocuSign. In every case (including this one) faxing the document back was acceptable, which breaks this. I am all for improving chain of trust, but it's not very helpful if the user doesn't understand what they're doing and as someone who likes tech I tend to want a bit more control than most people.
Incredibly important in many business processes not to mention signing contracts.
Another tactic is contracts signed by another authorizing action like "your check is as good as your signature language" or "Under the U.S. Uniform Electronic Transactions Act (UETA), this Agreement is executed electronically when both parties agree via e-mail, an Internet web page, or other electronic means and the Client pays the deposit as set forth in..."
A simple email saying I agree is acceptable under US law. No cryptographic PDF features necessary.
I'd never heard of Xournal, thanks!
Also note that those "hand signed" PDFs tend to not hold up to legal scrutiny unless they're also digitally signed.
[1] https://www.allens.com.au/globalassets/pdfs/insights/xmedia/...
However, in reality I've often found it easier to write throwaway perl scripts to analyse/modify PS files rather than PDF. Writing a tool to target a set of PS files made by the same process usually isn't too hard unless there is something really unique going on - but it can be a problem generalising it to any random PS file.
PDF is more structured so it can be easier to make general purpose tools, but in my line of work we prefer version 1.4 since the later versions add bloat that isn't necessary for print. It's also usually easier to consider them append-only, it's trivial to add content but editing is a lot harder due to offsets and references.
From my understanding, PDF is largely based on Postscript. PDF is to Postscript as HTML5 is to XHTML or HTML4.